The Complex Inner Core Boundary Beneath South America From Seismic Core Phases: Possible Elevated Topography and Fast Crystallization

Abstract Multi‐scale topography and elastic contrasts at the inner core boundary (ICB) are crucial for understanding inner core (IC) growth and outer core (OC) convection. However, most ICB studies focus on the IC's eastern hemisphere, with limited spectral constraints on ICB topography. Here, we analyze 261 highest‐quality core‐reflected pairs (PcP and PKiKP) to constrain ICB contrast and topography beneath the Americas. Differential travel time residuals, amplitude ratios, and spectrograms reveal a complex pattern beneath Central America and the Caribbean, likely influenced by lower mantle heterogeneities. In contrast, systematic latitudinal variations beneath South America suggest possibly elevated ICB topography (∼220 km length, 1.0–2.5 km height). We find ICB contrasts 10% larger than in the ak135 model (density: 0.57 g/cm 3 ; P‐velocity: 0.79 km/s). These findings suggest localized fast IC crystallization beneath South America, with one possible explanation being OC downwelling flow beneath the Circum‐Pacific belt, which elevates ICB topography and increases density contrast.